EFFECT OF AGING TREATMENT ON PITTING CORROSION AND CORROSION FATIGUE CRACK PROPAGATION BEHAVIOR OF OIL-GRADE ALLOY 718

In this study, the influence of aging treatment on pitting corrosion and corrosion fatigue crack propagation (CFCP) behavior of oil-grade alloy 718 in different NaCl solutions is investigated. Electrochemical measurement results show no change in the pitting corrosion resistance of alloy 718, regardless of aging treatment, indicated by the similar corrosion current density and pitting potential. The pitting corrosion resistance is decreased with the increase in solution temperature and NaCl concentration. CFCP results demonstrate that there is no effect of 3.5 wt.% NaCl solution on the CFCP rates of alloy 718 in comparison with the ones tested in air, in spite of aging treatment. Nevertheless, 21 wt.% NaCl solution produces a deleterious effect on the CFCP rates of alloy 718. Aging treatments lead to lower CFCP rates in all tested environments. However, no difference of CFCP rates is observed between one-step aged and two-step aged specimens.